In many applications it is necessary to provide two motor starters or contactors connected to energize the same electrical device from the same energy source. A typical application of this type may be found in a polyphase reversible motor.
There are known individual mechanical and electrical interlocking arrangements for avoiding simultaneous closure of both contactors. It is also known to provide starter circuits wherein components permit both electrically and mechanically interlocking. In general, mechanical interlocking devices may take the form of those shown in U.S. Pat. Nos. 3,240,889, 3,536,868 or 3,564,466, each of which are assigned to the assignee of the present invention. Devices for preventing the simultaneous closure of two or more control circuits have been known since the advent of the 1912 Bechoff U.S. Pat. No. 1,037,580. This concept has evolved into self-contained mechanical interlock assemblies, such as those disclosed in U.S. Pat. No. 3,510,612 granted to Ward, and in U.S. Pat. No. 3,210,491 granted to DiMarco. In both of the latter-mentioned assemblies, there is an provided arrangement for seating the self-contained unit between adjacent contactors.
In situations where both electrical and mechanical interlocking is deemed to be beneficial or necessary, as in the case of requirements in certain industry standards, wherein electrical interlocking requires separate auxiliary contacts individually attached to the contactors, occupying considerable space with extra wiring for connection of these auxiliary switches with the various terminals of the individual contactors.
From a practical and commercial standpoint, it is obvious that reduction in size of electrical control devices is a user convenience and often a requirement. Reversing motor starters are often contained within modular control centers where the user-customer expects such centers to be of a size suitable for locating a maximum number of control devices, wiring and adjunct equipment within a minimum amount of space.